title: Evidence for the existence of two distinct pools of intracellular calcium in the rat aorta accessible to mobilization by norepinephrine.
abstract: The contractile responses of isolated rat thoracic aortic strips to norepinephrine (NE) and KCl in the absence of extracellular calcium were studied using 1,2-bis-(2-dicarboxymethylaminoethoxy)ethane (EGTA) as a calcium chelating agent. Whereas aortic tissue which had been washed in EGTA-containing buffer was refractory to KCl, it remained biphasically responsive to stimulation by NE. The initial phasic contraction induced by NE was rapidly produced by short-lived, with the magnitude of the maximum tension produced in calcium-free medium (containing 1 mM EGTA) being approximately 26% of that induced by NE in the presence of extracellular calcium. This phasic component could not be elicited a second time in the same tissue unless the tissue was re-exposed to extracellular calcium. The second component of the NE response in calcium-free medium was a slowly developing and sustained contraction which represented 24% of the maximum contraction obtainable in calcium-containing medium. The sustained contraction could be repeatedly elicited in the same tissue even after 5 continuous hr in calcium-free EGTA medium. The two components of the biphasic response are dissociable and each is apparently dependent upon the mobilization of a distinct intracellular pool of calcium. However, a single initial mechanism appears to trigger the biphasic response to NE, with a probable involvement of the alpha adrenergic receptor.
mesh_terms: D000818:Animals; D001013:Aorta, Thoracic / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D004533:Egtazic Acid / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000378:metabolism; D009638:Norepinephrine / Q000494:pharmacology* / Q000502:physiology; D010646:Phentolamine / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D004533:Egtazic Acid; D011189:Potassium Chloride; D002118:Calcium; D009638:Norepinephrine; D010646:Phentolamine